Here are some strage the brak it up or up and down that is all i can think of if you whant more info then go to other blogers from my class ex:
if you took 6,692 - 789 = 5,903

if you brok up the 789 and ternd it in to the 700 brak it up in to 600 and 100 then leve the 80 and brak up the 9 in to 2 and 7 then...
work!
6,692 - 600 = 6,092
6,092 - 100 = 5,992
5,992 - 80 = 5,912
5,912 - 2 = 5,910
5,910 - 7 = 5,903